I designed my own board using the M95-R module. I powered the module by driving the PWERKEY pin in the 1.2 s low state. I sent AT commands by connecting the TX and RX pins of the module with USB TTL. The system worked without any problems. By inserting my sim card, I was able to send messages properly. I did not encounter any problems when I enabled the Uart line to communicate with stm. The ATI I sent, AT+CPIN? and AT+COPS? commands have been answered. But when I insert the sim card into the system I use with this stm, the module resets itself at certain intervals. I understand by watching the PWERKEY led when it resets. I think it’s not a hardware problem, but I couldn’t figure out where the problem might be. Thank you for your help in advance.
You are advised to restart the system as follows:
You can monitor the voltage of the VBAT pin (Pin33, Pin34 are both), this is the POWER supply pin, the module will automatically shut DOWN when it is lower than 3.45V, then the module should report UNDER_VOLTAGE POWER DOWN message, if the PWRKEY pin is low for a short time after the shutdown,The module will restart
Monitor the waveform or voltage of the PWRKEY pin to see if there is any fluctuation. When the module is running normally, if the PWRKEY pin is pulled down for more than 1.2s, the module will shut down